Various display units, such as a liquid crystal display, a plasma display (PDP), an organic EL display have been developed, and those screen sizes has been enlarged more and more. For example, in the fundamental constitution of a liquid crystal display, a polarizing plate is provided in one side or both sides of a liquid crystal cell. Since the polarizing plate allows only light having polarized wavefront with the specified direction to pass through, the polarizing plate bears an important role to visualize change of the orientation caused by an electric field in a liquid crystal display. Therefore, the performance of the liquid crystal display may be greatly influenced by the performance of the polarizing plate.
In the general constitution of the polarizing plate, for example, a protection film or a retardation film made of a cellulose ester films such as a cellulose triacetate film is pasted with an adhesive like a polyvinyl alcohol onto one side or both sides of a polarizer made of a polyvinyl alcohol film which has been uniaxially stretched and dyed with iodine. Furthermore, this polarizing plate is pasted on a liquid crystal cell with an adhesion layer.
A large-sized polarizing plate has been required with the enlargement of the screen of the above-mentioned display unit. However, when it was going to extend the width of the above-mentioned cellulose ester film used for this polarizing plate, it turned out that fracture failure takes place easily. Especially, in a widthwise stretching device called a tenter, when it is going to stretch a film with high draw ratio (draw or stretching magnification), in many cases, fracture takes place at the grasped portion of film width end portions by such as a clip and a pin of a tenter device, or the clip and the pin are disengaged from the grasped portion to cause manufacture failure. Therefore, a method of performing certainly widthwise grasping by a clip, a pin, etc. in the tenter device has been requested.
In order to prevent fracture, it may be considered that it is effective to make a stretching stress smaller. Usually, if a film is stretched on the condition that a solvent is remaining in the film formed by the solution casting film forming method, a stretching stress can be reduced. However, with this method, a portion of a film near the grasped portion becomes also soft, there may be a case where fracture increased on the contrary. To counter this, a method of making it hard to cause fracture by making the volatile component content in the film at the grasped portion smaller than that in the film at the central portion (for example, refer to Patent Document 1).
However, when the amount of remaining solvents at the ends of a film was reduced, there was a problem that curl at the ends of the film became larger to make it difficult to insert the film in a grasping tool.
Patent document 1: Japanese Patent Unexamined Publication No. 2002-127245